A copying machine, facsimile transmitter machine or the like is provided with a console panel having an inputting portion and a display portion. The console panel communicates with a main controller provided in a main body of the machine. There have been two communication techniques. One is a static communication technique and the other a dynamic scan communication technique.
In the static communication technique, the number of control lines are required which corresponds to the number of display elements or inputting keys, which consequently involves cumbersome wiring and needs an increased number of connectors.
In the dynamic scan communication technique, on the other hand, the inputting portion and the display portion of the console panel are connected to the main controller in the form of a matrix. A scan address and display data are transmitted to the display portion in which display elements are in turn driven in accordance with the transmitted scan address and display data to provide a dynamic display. Also, key data is transmitted to the main controller from the operation portion.
Accordingly, it will be seen that the dynamic scan communication technique needs smaller number of control lines than the static communication technique. However, in case the number of display elements or inputting keys increases, the number of control lines will increase. Consequently. wiring becomes cumbersome and an increased number of connectors are required. Moreover, the main controller needs more complicated program.
Japanese Unexamined Patent Publication No. 60-101561 has proposed a signal communication system in which a CPU is provided in an operating portion to execute nonsynchronous serial communication between the operating portion and a main controller. Specifically, only when display data is changed, the changed data is transmitted from a CPU in the main controller to the CPU in the operating portion in serial form, and stored in the CPU in the operating portion, and then displayed on a display portion. However, there is a likelihood that if the transmitting signal is distorted to an wrong signal by noise or the like in the transmission, the wrong signal is stored in the CPU, and displayed on the display portion. To prevent the above wrong display, the CPU of the operating portion executes the detection of wrong data, and transmits to the CPU of the main controller a signal requesting the re-transmission of display data when wrong data is detected.
However, the signal communication system of Japanese Unexamined Patent Publication No. 60-101561 has the following drawbacks: The request of re-transmission makes the signal processing more complicated, and also makes signal processing time longer. The provision of the CPU in the operating portion needs a program for the CPU of the operating portion, and increases the costs of production.
Also, in the dynamic scan communication technique, data is transmitted in a fixed order between the main controller and the operating portion. Accordingly, data having the same address is transmitted in the same cycle. If the power source, clock signal generator, or external unit generate a noise in synchronization with the transmitting signal, the noise will continuously damage data in a particular address. Consequently, a particular area of the display portion continuously provides a wrong display, or input of a particular key is continuously wrongly transmitted to the main controller.
There has been a signal communication system provided with CPUs in a main controller and an operating portion respectively, the CPUs checking every frame whether or not a received signal has an error. Specifically, the CPU of the operating portion executes checking of the received signal every one frame, e.g., 24 bits, and transmits an error flag data representing the detection result in the form of one bit to the CPU of the main controller. Similarly, the CPU of the main controller executes checking of a signal transmitted from the operating portion every one frame, and also confirms the error flag data from the operating portion. When it is detected based on the error flag data that the signal received by operating portion has no error, the CPU of the main controller transmits a next new signal to the operating portion. If it is detected that the signal received by the operating portion has an error, the CPU of the main controller transmits the previously transmitted signal to the operating portion again.
However, the CPU of the main controller executes the checking of a signal from the operating portion every frame. Even if the received signal has no more than one bit error, all the data in the checked frame are determined to be invalid. Accordingly, the checked frame including the error flag data is not received by the CPU of the main controller. Consequently, the CPU of the main controller does not transmit the previously transmitted signal again, which has been requested by the operating portion, but transmits a next new signal to the operating portion.
After receiving the error flag data, the CPU of the main controller determines whether it is necessary to transmit the previously transmitted signal is transmitted to the CPU of the operating portion again. Accordingly, a prolonged time is consumed for the signal communication, which consequently involves light flickerings in the display, and slow response in key inputting. Further, it will be seen that the more display elements and keys are provided, the more often the flickering and slow response will occur.
In view of the above-mentioned drawbacks, it is an object of the present invention to provide a signal communication system which is simpler in construction, and can ensure smaller number of communication error and higher communication speed.